1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method. In particular, the present invention relates to an application of a smoothing processing to an image and manner of the application.
2. Description of the Related Art
Recently, multi function machines including an ink jet print type printing mechanism and a scanner mechanism (hereinafter also referred to as IJMFP) have been widely provided. IJMFP is a printer that can be connected to a personal computer (PC) to provide various applications such as a function to perform printing and scanning, a copy function of the machine itself, and a function by which the machine is connected to a digital camera for direct printing. Thus, the multi function machines have been used as a copying machine for family use for example. The copy function of IJMFP reads a document image by a scanner mechanism to print the image on a printing medium such as a paper.
In the copying as described above, the color reproduction range and the like is generally different depending on the type of a document to be copied. Thus, there may be a case where the document and a copy output have difficulty in having identical visual colors. There may be another case where different gradation characteristics may be reproduced depending on the type of a document.
To solve this problem, Japanese Patent Laid-Open No. 2001-251513 proposes a technique using image region segmentation. Specifically, this publication describes a method for segmenting a read image to at least a halftone dot region and a photo region and subjecting the respective regions to optimal γ conversions to provide favorable images in all regions. Also, Japanese Patent Laid-Open No. 2002-218271 describes a method for similarly segmenting a read image to a character region and a photograph region and subjecting the respective regions to optimal color space conversions to provide favorable images in all regions.
When a copy is made on a plain paper through the IJMFP, since a color reproduction range by the plain paper is narrow compared with those of document images of a printed matter, silver halide photograph and the like, some color compression methods may cause deterioration in a gradation characteristic such as contouring and losing gradation. For such a problem, Japanese Patent Laid-Open No. H10-155087 discloses a method for detecting an edge amount of a character in an image and adding a random number to the image depending on the amount so that the contour in a continuous gradation can be suppressed without damaging the sharpness of characters. Similarly, Japanese Patent Laid-Open No. 2001-144943 discloses a technique according to which a region is set in a part of multivalued color image data to which random number data is added and the random number data is added only to the set region so that a gradation jump is corrected and original images in the remaining regions are maintained.
As described above, there has been a problem in which an input image such as a document image in the case of a copy has a different color reproduction range from that by a printing apparatus. This problem has been generally addressed by the use of a color compression technique. However, when a color reproduction range is narrow as in the case where a plain paper is used in the ink jet method, it is difficult for a single color compression method to realize an optimal color reproduction for both of a character image and a photograph image. For example, when a color compression is performed with a high contrast so as to clearly represent characters, a photograph subjected to the same color compression may lose the gradation in a high density region and a high chroma region. On the other hand, when a color compression in which an importance is placed on the gradation characteristic is carried out so as not to break the gradation of a photograph image, characters subjected to the same color compression may have black characters or the like which are printed in a further lighter color. Specifically, characters written by a pencil that have a low density, characters that are not the so-called solid-black ones, or black characters outputted to a plain paper based on the ink jet method are printed in further lighter color, thus clear characters cannot be outputted.
In order to realize the printing of both of character images and photograph images, Japanese Patent Laid-Open No. 2001-251513 and Japanese Patent Laid-Open No. 2002-218271 have been proposed as described above. However, when a plurality of color compression tables or a gamma processing tables are switched and used for the respective images, a problem is caused where a memory for retaining tables suitable for the respective character and photograph images are required.
As methods in which a processing is changed depending on an image area without increasing tables, Japanese Patent Laid-Open No. H10-155087 and Japanese Patent Laid-Open No. 2001-144943 has been proposed as described above. However, the techniques described in these publications add noise to a part at which a contour is caused to improve the gradation reproduction characteristic and thus eliminates an originally-caused contour. Therefore, these techniques are not a technique that considers an influence by a subsequent image conversion to reduce the effect of the image conversion processing.